Generally speaking, tissue engineering involves a combination of living cells and a support structure called a scaffold. The scaffold, depending upon the tissue being produced, can be anything from a matrix of collagen, a structural protein, to a synthetic biodegradable polymer laced with chemical and biological cues that stimulate cell growth and multiplication. The cells initiating the process can come from laboratory cultures or from the patient's own body. The role of the scaffold (to induce surrounding tissue and cell ingrowth and/or to serve as matrices for transplanted cells to attach, grow and differentiate) is temporary, but important to the success of producing engineered tissues.
An ideal tissue engineering scaffold is biocompatible, biodegradable, porous, functionalizable and mechanically strong. Tissue scaffolds can be used to repair defects in hard tissues (such as bone) or soft tissues.
Bone grafting applications can be differentiated by the requirements of the skeletal site. Certain applications require a “structural graft” in which one role of the graft is to provide mechanical or structural support to the site. Such grafts should be fabricated of a material capable of providing the strength needed for load-bearing. The graft may also have beneficial biological properties, such as incorporation into the skeleton, osteoinduction, osteoconduction, and/or angiogenesis.
For areas of the body in which the mechanical load-bearing requirements of an implant can be challenging, lack of replacement by host bone tissue can compromise the implant by subjecting it to repeated load and cumulative unrepaired damage (mechanical fatigue) within the implant material. Thus, it is highly desirable that the implant have the capacity to support load initially, and be capable of gradually transferring this load to the host bone tissue as it remodels the implant.